This invention is directed to a novel method for preparing an aromatic bisimide by a process of effecting a reaction between a 3-substituted N-arylphthalimide and an aromatic dihydroxide dianion. More specifically, this invention relates to a simplified method for preparing an aromatic bisimide by effecting a reaction between a 3-substituted N-arylphthalimide and an aromatic dihydroxide dianion in a non-polar solvent without the use of a phase transfer catalyst.
Aromatic bisimides are valuable precursors for the synthesis of polyetherimides (See for example, U.S. Pat. Nos. 4,011,198 and 3,905,942, both issued to Takekoshi et al. in 1977 and 1975, respectively). Polyetherimides have a wide variety of uses such as in automobile parts, airplane parts, insulation for wires and various components for electrical appliances and the like. Polyetherimides also can be blended with other thermoplastic elastomeric resins to improve their physical properties, such as flame retardance, blow moldability and resistance to crack.
It is well known that the reaction of N-alkylnitrophthalimides, such as 4-nitro-N-methylphthalimide (4-NPI), with phenoxide salts, such as the disodium salt of bisphenyl-A (BPA), requires the use of a phase transfer catalyst, such as tetrabutyl ammonium bromide and/or a dipolar aprotic solvent, such as dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF). In fact, in the absence of either a dipolar aprotic solvent or a phase transfer catalyst, the reaction between the disodium salt of BPA and 4-NPI in a non-polar solvent, such as toluene, does not occur even after several hours of refluxing.
U.S. Pat. No. 3,992,406, issued to Markezich in 1976, for example, describes a method for preparing aromatic bisimides by effecting a reaction between a 3- or 4-nitro-N-substituted phthalimide with an aromatic dihydroxy compound in a dipolar aprotic solvent. The dipolar aprotic solvent is selected from the class consisting of dimethyl sulfoxide, N,N-dimethyl acetamide, N,N-dimethyl formamide (DMF), N-methyl pyrrolidone and mixtures thereof. Markezich's reaction is also carried out in the presence of an alkali-metal fluoride such as a fluoride selected from the class consisting of potassium, cesium and rubidium fluorides.
U.S. Pat. No. 4,017,511, issued to Williams, III in 1977, also describes the preparation of aromatic bisimides by reacting a 3- or 4-nitro-N-substituted phthalimide with an aromatic dihydroxy compound. Williams's reaction is carried out in the presence of an alkali-metal hydroxide and a dipolar aprotic solvent, e.g., dimethyl formamide.
The above current methods however incur costs. Dipolar aprotic solvents are expensive, very difficult to recover and purify and are moderately toxic. Phase transfer catalysts are also expensive and difficult to recover, and in addition partially decompose during a reaction, thereby affording nitrosamines which are known carcinogens. Consequently, there is a need for a more economic and safer method for preparing aromatic bisimides.
Surprisingly, it has now been discovered that aromatic bisimides can be produced without the use of the phase transfer catalyst or dipolar aprotic solvent. Specifically, 3-substituted N-arylphthalimides can be reacted with an aromatic dihydroxide to give excellent yields of an aromatic bisimide by refluxing in a non-polar solvent. Consequently, the present process is less expensive and eliminates the hazards found in prior methods.